Review of the latest research on coal, environment, and clean technologies

Abstract

Fossil fuels, coal in particular, are indispensable sources of energy necessary for today's technological and economical progress throughout the world. Their burning releases numerous environmental contaminants, like CO 2 , SO 2 , and a range of organic and inorganic compounds. Arguably, however, and despite the fact that these emissions have resulted in air pollution and regional acid rain problems, there is no evidence yet of their usage completely replaced by a low-CO 2-producing energy source. Coal, due to its unique composition and characteristics, has been actively investigated by scientists and technologists from various disciplines in a search for economically valuable metals and medically active substances. Also, coal is used universally for the fabrication of new nanomaterials in laboratories, and utilized in waste-treatment and clean-coal technologies. The aim of the paper was to focus on the latest advancements in coal research of leading international scientists from India, China, and USA. Also, the paper is briefly presenting selected papers of several Indian and Croatian research groups addressing environmental issues and emerging waste-treatment technologies. Although the two countries are different from the geographical, historical, economical, and industrial point of view, the both have been linked with the coal extraction and its usage in power generation and associated heavy industries.

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Corresponding author: Gordana Medunić
gmedunic@geol.pmf.hr
The Mining-Geology-Petroleum Engineering Bulletin
UDC: xxx:xx (author’s propose)
DOI: 10.17794/rgn.xxxx.x.x (filled by editors)
paper category (filled by editors)
Review of the latest research on coal,
environment, and clean technologies
Gordana Medunić1; Deepti Mondol2; Ankica Rađenović3; Sadhana Nazir4
1University of Zagreb, Faculty of Science, Department of Geology, Zagreb, Croatia
(Associate Professor)
2Ewing Christian College, Zoology Department, Allahabad, India (Assistant
Professor)
3University of Zagreb, Faculty of Metallurgy, Sisak, Croatia (Full Professor)
4Pandu College, Zoology Department, Guwahati, India (MSc)
Abstract
Fossil fuels, coal in particular, are indispensable sources of energy necessary for today's technological and economical
progress throughout the world. Their burning releases numerous environmental contaminants, like CO2, SO2, and a
range of organic and inorganic compounds. Arguably, however, and despite the fact that these emissions have resulted
in air pollution and regional acid rain problems, there is no evidence yet of their usage completely replaced by a low-
CO2–producing energy source. Coal, due to its unique composition and characteristics, has been actively investigated by
scientists and technologists from various disciplines in a search for economically valuable metals and medically active
substances. Also, coal is used universally for the fabrication of new nanomaterials in laboratories, and utilized in waste-
treatment and clean-coal technologies. The aim of the paper was to focus on the latest advancements in coal research of
leading international scientists from India, China, and USA. Also, the paper is briefly presenting selected papers of
several Indian and Croatian research groups addressing environmental issues and emerging waste-treatment
technologies. Although the two countries are different from the geographical, historical, economical, and industrial point
of view, the both have been linked with the coal extraction and its usage in power generation and associated heavy
industries.
Keywords: coal, waste, environmental pollution, clean-coal technology, bioremediation.
1. Introduction
Coal is the most abundant specimen among the fossil fuels, i.e. the coals, oil shales, oil, and gas deposits of Earth. It
is the deposit of organic matter – the remains of dead plants and animals – entrapped in sedimentary rocks at the site of
organic matter growth many millennia ago. Coals generally contain 10-30% of inorganic material made up of clay
minerals, quartz silt, and sand, thus contributing to metal emission load upon their combustion (Saikia et al., 2009;
Singh et al., 2015a; Dai et al., 2016). By igniting coal, the Sun energy stored in it is being released, thus producing heat
and energy needed for industry, and generally, sustaining nations' standards of living. However, the fuel burning
emissions are the largest source of anthropogenic greenhouse gases and aerosols (Kumar et al., 2017a). Also, some
European and Asian countries have experienced devastating damage to the environment and to the human health owing
to many years of intensive coal mining/burning and associated metallurgy in the past (Helios Rybicka, 1996; Sofilić et
al., 2013; Oliveira et al., 2014; Banerjee et al., 2016; Naik, 2016). Notwithstanding, in the current situation of high-
energy demand, coal still remains a vibrant industry. According to the World Coal Association (WCA), proven reserves
of coal are much greater than those of oil and gas combined, and are sufficient to supply more than 100 years of
production at 2015 levels. However, Höök et al. (2010) emphasize that a peak in global coal production should be
reached in the 2020-2030, and that 'This is much sooner than commonly thought, and if this is correct it would represent
a significant challenge for future energy supplies'. Furthermore, the latest WCA reports note that coal still makes up
29% of global primary energy and 41% of global electricity.
Coal, being the most important energy source in parts of the world lacking pollution-control technology, adversely
affects global atmosphere (Banerjee et al., 2016). It is the most complex geological material, composed of organic
compounds (Saikia et al., 2007), H2O, oil, CH4, and all the chemical elements, together with a wide variety of minerals
(Finkelman, 1994; Rađenović, 2006). According to the 1990 US Clean Air Act Amendments, the hazardous trace

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elements As, Be, Cd, Co, Cr, Hg, Mn, Ni, Pb, Sb, and Se are listed as key toxic air pollutants (U.S. EPA, 1990). The
original US Clean Air Act, implemented by the Environmental Protection Agency in 1971, and the amendments to the
act in 1977 and 1990, have required a substantial evolution of the quality of coal in terms of the reduction of SO2 and
NOx emissions (Hower et al., 1999). Low-quality coals have high ash, high sulphur, and high trace element contents.
Due to stringent environmental regulations, various physical, chemical, and microbiological methods have been
developed to solve the hazardous impact of these substances on the environment (Rađenović, 2004; Mishra et al.,
2007; Singh et al., 2013, 2014; Baruah et al., 2016; Saikia et al., 2016; Kumar et al., 2017b). Also, the combustion
behaviour of various types of coal is dependent on their ash properties (Mishra et al., 2016).
Previously, Rađenović et al. (2016a) outlined comparative information on geography, meteorology, industry and
environmental policy in Croatia and India. Briefly, Croatia is a southeastern European country, having a total area of
56,542 km2, and sharing boundaries with six countries the length of which is 2,375 km. On the other hand, the total area
of Republic of India is 3,287,590 km2, which is nearly 60 times larger than Croatian territory. The total length of
boundary with neighboring countries is 21,103 km, i.e. nearly 9 times Croatian boundaries, of which 7,000 km is
coastline. In relation to coal, the most important as well as the largest coal-mining (superhigh-organic-sulphur Raša
coal, SHOS) area in Croatia (Medunić et al., 2016a) is situated at the eastern part of the Istrian peninsula (Fig. 1 in
Rađenović et al., 2016a). It was exploited from 18th century till late 1990s. There is also a location of the sole Croatian
coal-fired Plomin power plant (PPP), which started with operation in 1970 using SHOS Raša coal enriched in S, up to
13-14% (Medunić et al., in press), while imported low-S coal has been used for the last 17 years. India, having almost
7% of the world’s total coal reserves, belongs to the so-called Big Six group, i.e. USA, Russian Federation, China,
India, Australia, and South Africa. These countries account for nearly 80% of the world’s coal production, with 43%
from China alone. Coal has been mined in India for more than 230 years (Höök et al., 2010). The Integrated Energy
Policy Committee, set up by the Government of India in 2004, has emphasized the continuing dominance of coal in
Indian Energy Sector over the next 25 years. According to Geological Survey of India, the coal reserves in India are
estimated to be some 308.802 billion tons, extending up to depths of 1,200 meters. Only 12.5% of them belong to the
coking type, while the remaining 87.5% is thermal coal. They are mainly distributed in the states of Bihar and
Telangana. Chikkatur et al. (2009) note that coal currently accounts for more than 50% of total primary commercial
energy supply in the country and for about 70% of total electricity generation. According to these authors, the ash
content in Indian coals have been increasing over the past three decades, primarily because of increased opencast mining
and production of coal from inherently inferior grades of resources. As a consequence of the high ash content in Indian
coals, at least 4,047 m2 of land is needed to store ash per one MW of installed capacity, and there are many large power
plants with more than 4,047,000 m2 of land dedicated only for ash storage (Chikkatur et al., 2009). The authors
conclude that good coal-power policies encompass following measures: improving the efficiency of all elements of the
country’s existing power system, deploying high efficiency technologies in the short term, and devising a long-term
strategy for developing and deploying advanced coal power technologies.
The objectives of the paper are to present the latest advancements in coal research, carried out by leading
international scientists from India, China, and USA, and to outline selected Indian and Croatian studies addressing
environmental contamination and waste-treatment technologies.
2. The latest multidisciplinary environmental and clean-coal technology research in India,
China, and USA
Detrimental impacts of coal mining, coal combustion, and coal by-product disposal on the environment are well
documented in scientific literature. They are mainly related to acid-mine (S) drainage problems (Burgos et al., 2012),
selenium (Se) leaching from ash, and its concomitant mobility (Dreher and Finkelman, 1992; Harkness et al., 2016),
and soil, air, and water pollution (Baruah et al., 2006; Oliveira et al., 2014; Saikia et al., 2015a; Nišić et al., 2016).
That was inevitable due to lack of a proper legislative and non-existent clean-coal technologies in the past. Today, the
situation is getting substantially improved from the both points of view. The society members are aware of the fact that
energy is necessary, and coal resources are in a high demand for that purpose. Therefore, clean-coal technologies are
being actively developed throughout the world coal laboratories and implemented in industrial devices. Coal is also
necessary for various technological and medical utilizations and applications, and this statement will be elaborated by
the following text.
Briefly, clean-coal technologies are focused on the removal of mineral matter (ash yield) and sulphur from coal.
Sulphur emissions generate hazardous sulphate aerosols and corrode the boiler tubes during operation. The mineral

Medunić, G., Mondol, D., Rađenović, A., Nazir, S.
The Mining-Geology-Petroleum Engineering Bulletin and the authors ©, DOI: 10.1177/rgn.xxxx.x.x)
matter in coal forms ash upon its combustion (Saikia et al., 2015b) what is disadvantageous due to slagging, abrasion
and fouling, leading to ash fusion inside the boiler. Moreover, leaching of potentially toxic trace elements from ash
makes them bio-available, while the emission of micron- and nano-size ash particles degrade the quality of environment
and human health (Kumar et al., 2015). An Indian (Assam) coal chemistry group, led by Binoy K. Saikia, has been
actively working on the production of advanced carbon materials from cheap bio-stock, such as low-grade coals and
waste carbon materials, for advanced applications in the society. Also, they are focused on energy and environment
topics. Herewith, Saikia et al. (2014) demonstrate the application of ultrasonic energy (20 kHz) to a few high-S Indian
coals in aqueous and mixed alkali media (1:1 KOH and NaOH) in order to remove S and ash for the various industrial
applications. The study showed maximum ash, pyritic S, sulphate S, and total S removal as follows: 87.52%, 83.92%,
12.50%, and 18.80%, respectively. The XRD and FTIR spectral analyses revealed the reduction in ash and different
forms of S by use of ultrasonic energy. According to the ash fusion temperatures and the calorific values of the
ultrasonicated coal samples, the quality of coal was greatly improved, while the coal leachates after ultrasonication were
found to be predominant in non-hazardous K, Ca and Mg. Furthermore, Saikia et al. (2016) applied the ultrasonic
energy in an aqueous H2O2 medium to remove S and ash from Brazilian coal. The study showed the maximum removal
of 87.52% total S. The authors demonstrated how to replace other conventional clean-coal technologies in terms of less
energy, less treatment time, less reagent volume, and low reagent concentrations. Noteworthy, they suggest that the
method may be used in larger-scale trials with high-S and high-ash coals worldwide for a long time, due to partially
green nature of the procedure. In the study carried out by Saikia et al. (2014), ionic liquids were examined for the
extractive desulphurisation and de-ashing of high-S sub-bituminous Indian coals. The ionic liquids, 1-n-butyl-3-
methylimidazolium tetrafluoroborate and 1-n-butyl 3-methylimidazolium chloride, were employed in the presence of
HCOOH/H2O2 and V2O5. The maximum removal values were following: 50.2% total S, 48.0% organic S, and 70.3 wt%
ash. Hereby, the study demonstrated high efficiency of removing significant amounts of inorganic as well as organic
sulphur (aryls) components from the originally high-S coal. Apart from being a target for cleaning technology
experiments and geochemical investigations, coal has been used for the production of advanced carbon materials. Das et
al. (2017) report results of their study on supercapacitor electrode materials produced from low-grade coal by using wet-
chemical methods. Namely, the authors note that there is a growing need to develop new types of clean and sustainable
energy conversion and storage systems, such as batteries and supercapacitors for electric vehicles with low exhaust
emissions. They also emphasize that supercapacitors are energy storage devices which have received tremendous
attention due to their high power density, short charging time, and long cycling life, thus achieving the better fuel
economy, decreasing harmful emissions, and reducing the reliance on petroleum sources. Moreover, Das and Saikia
(2017) fabricated carbon nanomaterials, i.e. nanodiamonds from low-grade coals during low-power ultrasonic-assisted
stimulation in hydrogen peroxide followed by dialysis in 1 kDa. These nanomaterials have promising applications in
bioimaging engineering, photovoltaics, and optoelectronics.
Biological bioremediation approach, by using microorganisms to transform or degrade contaminants to make them
environmentally non-hazardous, is regarded as a cost-effective remediation technology appropriate for large polluted
soil and water areas. It has been successfully employed and developed by Indian scientists from Banaras Hindu
University (BHU, Varanasi, Uttar Pradesh), Professors Prakash K. Singh and Asha Lata Singh. They have been using
mixed bacterial consortium to explore the possibility of removal of potentially toxic trace elements from coal (Singh et
al., 2012a, 2015b). They have found out that the removal efficiency was more than 80% for Ni, Zn, Cd, Cu, and Cr, and
45% in case of Pb. The authors have also been working on desulphurisation of coal by using microorganisms Ralstonia
sp and Pseudoxanthomonas sp (Singh et al., 2012b). One of their latest papers (Singh et al., 2017a) presents the results
of the petrological coniderations in relation to the demineralization of Rajmahal Gondwana coals by means of
Pseudomonas mendocina B6-1. Following the treatment, a significant reduction in the elemental content of oxygen,
hydrogen and sulphur was observed. A gradual reduction of pyrite phase due to bioleaching was identified and its
signatures were reflected in XRD spectra and FTIR absorption bands. The authors also determined that some minerals
occur intergrown with inertinites, thus causing the restricted bacterial action due to inadequate exposure of mineral
particles and less surface area available for bioleaching. Also, their latest paper (Kumar et al., 2017b) reports the
results of demineralization of the Karanpura Gondwana coals enriched in ash (30.57%–21.80%) and low in sulphur
(0.29%–0.20%). They treated coal with Pseudomonas mendocina strain B6-1. The optimum conditions for effective
demineralization were following: pH 6.0, temperature 35°C, 6.0% (w/v) of pulp density, and incubation time of 7 days.
Moreover, the treatment proved to increase the useful heat value, gross calorific value and net calorific value of coal.
Hereby, the authors showed that their methodology was eco-friendly and useful in obtaining clean fuel.
In China, the coal consumption for power generation had increased from 196 Mtce in 1991 to 684 Mtce in 2005, and
the ratio of coal used for power generation relative to the total coal consumption increased from 26.0% to 44.6% in the

Medunić, G., Mondol, D., Rađenović, A., Nazir, S.
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same period (Chen and Xu, 2010). The authors outlined clean-coal technologies in China, presenting supercritical and
ultra-supercritical boilers, circulating fluidized bed combustion, integrated gasification combined cycles, together with
R&D trends, and demonstration on carbon capture and storage technologies. The leading Chinese coal researcher
Professor Shifeng Dai is actively investigating geochemical features of coal, specifically in the context of exploitation of
economically important trace elements (Dai et al., 2016). Also, Dai and Finkelman (2017) elaborate the fact that coals
are economic sources of strategically important elements, such as Ge, Ga, U, V, Se, rare earth elements, Y, Sc, Nb, Au,
Ag, and Re, as well as base metals Al and Mg. Their extraction and utilisation from coal could result in a number of
benefits, which will make this source an economically and environmentally attractive option, especially in China, USA,
Russia, India, and other major coal user countries for the foreseeable future.
The leading US coal petrology and coal geochemistry researcher is James C. Hower (UKY, Lexington, Kentucky).
He and his domestic as well as international co-authors are actively studying coal from all around the globe. To name a
few papers, they investigate distribution of REEs (Hower et al., 2016a, b), and U and radionuclides (Hower et al.
2016c) in coal, and Hg content in fly ash (Hower et al., 2017). Also, he participated in a medical multidisciplinary
study carried out by Wang et al. (2014). The authors carried out the isolation and structural elucidation of a new
tetracyclic polyketide (ruthmycin) from Streptomyces sp. RM-4-15, a bacteria isolated near thermal vents from the Ruth
Mullins underground coal mine fire in eastern Kentucky. Preliminary in vitro antibacterial, anticancer and antifungal
assays revealed ruthmycin to display moderate antifungal activity. A multidisciplinary study, carried out by an
international research group (Yang et al., 2017), reports that the coal combustion results in large quantities of otherwise
rare Magnéli phases (TixO2x–1 with 4 ≤ x ≤ 9) from TiO2 minerals naturally present in coal. The authors note that this
provides a new tracer for tracking solid-state emissions worldwide from industrial coal-burning. In its first toxicity
testing, they have shown that nanoscale Magnéli phases have potential toxicity pathways that are not photoactive like
TiO2 phases, but instead seem to be biologically active without photostimulation. The authors suggest that these phases
should be thoroughly tested for their toxicity in the human lung. Regarding clean-coal technologies in USA, Ruth
(2014) discusses them by presenting gasification, gas purification and separation, combustion turbines, fuel cells, and
advanced steam cycles, that are likely to play key roles in the design of near-zero emission plants. The author elaborates
critical materials, e.g. refractory linings for coal gasifiers, gas filters and sorbent systems to remove contaminants,
ceramic membranes for separating oxygen from air and hydrogen from carbon dioxide, blading and other components
for high-temperature combustion turbines, fuel cell electrodes and electrolytes, and boiler tubing and turbine
components for advanced steam cycles.
3. Indian research related to coal, environment, and technology
Unlike Croatia, coal petrology and coal geochemistry research in India is a very active scientific discipline, and one
of the leading experts is Professor Prakash K. Singh (BHU), whose few latest papers are briefly introduced here. Singh
et al. (2017b) adopted an integrated approach to study the lignite deposits of Surkha mine associated with the
Khadsaliya Clays Formation (Eocene) of Saurashtra Basin, western India. Organic petrographic, palynofacies and
geochemical data of the sampled succession have been acquired and discussed. Additionally, the authors used
palynological and biomarker evidences to infer the organic composition, quality, thermal maturity, origin and
depositional environment of the Surkha lignites, including the hydrocarbon source potential of the lignite-bearing
sequence. Singh et al. (2017c) investigated the lignite deposits of the Cambay basin of Gujarat in order to understand
their petrological and geochemical attributes, as petrological data about them are scarce compared to the wealth of
literature available on Indian Gondwana coals. Singh et al. (2017d) carried out investigations on the lignite deposits of
Kachchh Basin. The petrographic analysis of the lignites indicates a dominance of huminite group of macerals which is
mainly contributed by ulminite-A, ulminite-B, attrinite, densinite, and phlobaphinite. The mineral matter is present in
moderate concentrations, while S content is high. The study indicates on conditions of flooded forest swamps with a few
drier periods.
Environmental sustainability in India has been investigated by a BHU research group led by Professor Tirthankar
Banerjee. They measure atmospheric trace gases and aerosols from various observational platforms, aiming to predict
changes in atmospheric constituents and their repercussions on the climate. Herewith, their paper (Banerjee et al.,
2016) explores the possibility of a policy revision regarding clean air quality in recently launched nationwide campaign,
Clean India Mission. According to them, India has reasonably progressed in developing sanitary facilities and
disseminating clean fuel to its urban households, but the situation in rural areas is still miserable and needs to be
reviewed. Also, several policy interventions and campaigns were made to improve the situation, but the outcomes have
been remarkably poor. In conclusion, the authors recommend effective policy revision to disseminate clean energy,
especially to rural people, and to assess human health impacts from air pollution.

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Waste-water treatment technologies are being actively developed in India by numerous researchers. One Jaipur
group is led by Professor Neha Sharma. Their paper (Sharma et al., 2013) presents the results of an investigation of
textile wastewater in Rajasthan. By means of isolation and characterization of the indigenous bacterial strains which
would decolourise textile diazo dye, the authors isolated 10 bacterial strains and screened them for their dye
decolourising efficacy. The efficacies of bacterial strains were following: Staphylococcus sp. 82.5%, Serratia sp. 84.0%,
and Micrococcus sp. 76.5%. Sharma et al. (2017a) outline a potential of microorganisms to clean and modify the
complex organic compounds, which are xenobiotic in nature, to simple water soluble products by a process of
biomineralization. They elaborate how this capability largely depends upon the selective microbial community as well
as on the structural and functional groups of toxic compounds. The microorganisms may be either indigenous to a
contaminated area or isolated from elsewhere and brought to the contaminated site. The authors point out that different
enzyme systems and genes are responsible for the degradative bioprocesses in waste water systems. Also, the diversity
based studies should demonstrate a breakthrough in microbial ecology and environmental biotechnology domains.
Furthermore, Sharma et al. (2017b) shows how bio-nanotechnological solutions can be of a paramount importance in
circumventing the issues associated with wastewaters. The authors demonstrate a great potential of nanoparticles in
wastewater treatment. Their unique characteristic of a high surface area can be used efficiently for removing toxic metal
ions, disease causing microbes, organic and inorganic solutes from wastewater. Various classes of nanomaterials include
metal-containing nanoparticles, carbonaceous nanomaterials, zeolites and dendrimers. The paper presents a
comprehensive review of recent advances on different nanomaterial based mitigation strategies. A special emphasis was
given to a green synthesis of nanoparticles aimed to address problems associated with waste-water effluents through the
nano-bioremediation.
4. Croatian research related to coal, environment, and technology
Coal petrology research does not exist in Croatia at all as the coal mining (SHOS Raša) ceased altogether some 17-20
years ago. Coal studies have been mainly focused on detrimental consequences of SHOS Raša coal mining and
combustion (Medunić et al., in press) on the environment of the PPP area (Fig. 1 in Rađenović et al., 2016a). It has
been a major source of the Croatian energy production since early 20th century. Due to high values of S, PAHs
(polycyclic aromatic hydrocarbons), and radioactivity in coal, soil around the PPP was found to be severely polluted
with S and PAHs (Medunić et al., 2016b) as well as with Ra-226 (Ernečić et al., 2014), while Fiket et al. (2016)
determined peculiar REE patterns in studied soil samples. PAHs are typical products of anthropogenic processes (Naik,
2016). Their total concentrations in topsoil varied from 31 ng/g in control soil samples, to 13,535 ng/g at a distance of
100 m from the PPP (Medunić et al., 2016b). The authors ascribed PAHs mainly to the coal-combustion processes, and
to the additional contribution from a nearby unburnt coal pile subjected to casual very strong NE winds. Also, several
conference abstracts have been published lately on various topics related to environmental pollution derived from SHOS
Raša coal mining (Medunić et al., 2016c), distribution of sulphur isotopes in soil and coal (Malenšek et al., 2017), and
human health risk assessment indices (Medunić et al., 2017a, b).
Frančišković-Bilinski et al. (2017) described magnetic and chemical properties of karstic river sediments
contaminated by discharge of coal bottom ash and ash. They found very high magnetic susceptibility close to the
pollution source, and strong correlations with Co, Fe, Sr, Al, U and B. Oreščanin et al. (2012) analysed fly and bottom
ash in a former sulphate pulp factory. Compared to the world’s average soil concentration, U and Th values were
increased 3.7 and 1.7 times, respectively. The mean value of the total effective dose rate measured in the air at the
height of 1 m for all samples of ash and soil under the influence of the landfill was 1.60 mSv/yr. Compared to the
Croatian average (0.7015 mSv/yr), the determined mean value for the landfill was double. However, the mean value of
the total effective dose rate measured above the landfill was 11.4 times the local background (0.14 mSv/yr). The authors
suggested that the fly and bottom ash landfill should be sealed with 10 cm thick layer of the material with low
permeability to prevent redistribution of the radionuclides and heavy metals from the deposited material into the
environment. Sofilić et al. (2013) investigated soil at an old metallurgical landfill site exposed to direct influence of
metallurgical non-hazardous waste for many years. The obtained results point at contamination of soil with Cu
according to the legislation of all observed EU countries, with Cd according to the legislation of Italy, Poland, and
Belgium (Wallonia), and with Cr according to the legislation of Finland and Poland.
Regarding waste-water treatment technologies, Rađenović et al. (2013) analysed ladle furnace slag (LFS), which is a
byproduct from further refining molten steel after coming out of a basic oxygen furnace or an electric arc furnace. The
authors determined that the LFS proved to be an effective adsorbent for the removal of toxic metal ions from various
industrial waste-waters. They also point out that the slag is a cheap and abundant, non-hazardous industrial waste as the
ecotoxicity evaluation of its eluate showed that it did not contain constituents which might in any way adversely affect

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the environment. Furthermore, Rađenović and Medunić (2015) investigated removal of Cr(VI) from aqueous solution
by a commercial carbon black. By testing adsorbent dose, solution pH, contact time, initial metal concentration, and
temperature, the authors found out that an initial solution of pH 2.4 was most favourable for the Cr(VI) removal. The
equilibrium data best fitted the Freundlich isotherm model, while the maximum adsorption capacity was found at 33.22
mg/g. The thermodynamic parameters showed that the Cr(VI) adsorption on the carbon black was the spontaneous
exothermic process. Rađenović et al. (2016b) examined adsorption potential of the LFS for the Cr(VI) ions from
aqueous solutions. They found out that the value of their maximum removal was 22.3 mg/g at pH 4.3 and temperature of
293 K. It was determined that the Cr(VI) adsorption mechanism was complex, while the film diffusion, and the intra-
particle diffusion both contributed to the rate-determining step. Regarding the thermodynamic parameters, i.e. free
energy change, enthalpy change, and entropy change, it was revealed that the Cr(VI) adsorption onto the LFS was
endothermic and spontaneous.
5. Conclusions
The paper introduced several the most intriguing and advanced topics in coal research, carried out by leading scientific
authorities in India, China, and USA. It showed versatility and importance of this material which is still vibrantly
powering industries as well as scientific research. The paper also briefly summarised the latest Indian and Croatian
research on coal, environment, and clean technologies from various aspects and domains. It is evident that Indian coal
and technology research articles far exceed the Croatian ones, not only in terms of their total number, but also in relation
to the strength and novelty of research topics. However, this paper, having resulted from an Indian-Croatian
collaboration, exemplifies that future collaborations among environmental and chemical scientists as well as
technologists from the two countries should be more intensive. Herewith, the Croatian environmental and clean
technology science could advance towards the better perception by international scientists; also, some new collaborative
initiatives should connect more closely Indian scientists with their peers in EU.
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Abstract in Croatian
Pregledni rad o najnovijim istraživanjima ugljena, okoliša i čistih tehnologija
Fosilna goriva, posebno ugljen, neophodni su izvori energije potrebni za današnji tehnološki i ekonomski napredak
diljem svijeta. Njihovim spaljivanjem oslobađaju se brojni onečišćivači okoliša, poput CO2, SO2, te niz organskih i
anorganskih spojeva. Međutim, iako su te emisije rezultirale zagađenjem zraka i problemima regionalnih zakiseljavanja
oborina, ipak se ne može dokazati da je njihova uporaba u potpunosti zamijenjena izvorom energije koji bi ispuštao
niske razine CO2. Ugljen, zbog svog jedinstvenog sastava i obilježja, aktivno istražuju znanstvenici i tehnolozi iz
različitih disciplina, u potrazi za ekonomski vrijednim metalima i medicinski aktivnim tvarima. Isto tako, ugljen se rabi
u izradi novih nano-materijala u laboratorijima, te za potrebe tehnologija obrade otpadnih voda i proizvodnje čistog
ugljena. Cilj rada bio je usredotočiti se na najnovija dostignuća istraživanja ugljena vodećih međunarodnih znanstvenika
iz Indije, Kine i SAD-a. Također, u radu su ukratko predstavljeni odabrani radovi nekolicine indijskih i hrvatskih
istraživačkih skupina koje se bave pitanjima zaštite okoliša i novih tehnologija za obradu otpada. Iako se dvije zemlje
razlikuju u zemljopisnom, povijesnom, ekonomskom i industrijskom smislu, obje su imale izvjesnu vezu s
pridobivanjem ugljena i njegovom uporabom u proizvodnji električne energije te pripadajućim teškim industrijama.
Ključne riječi: ugljen, otpad, onečišćenje okoliša, tehnologija čistog ugljena, bioremedijacija
Acknowledgment
The first author (G.M.) is especially indebted to Dr. Massimo Zacchini (Italian National Research Council, Institute of
Agro-envinronmental and Forest Biology IBAF, Rome, Italy) and Dr. Paras Pujari (CSIR-NEERI, Water Technology
and Management Division, Nagpur, India) for their efforts while managing the TECO project (the Indo-Italian research)
which is funded by the European Union - Delegation of the European Union to India in collaboration with the
EuropeAid Cooperation Office. Thanks to the TECO grant ("EU-India project TECO ICI+/2014/342-817-Technological
eco-innovation for the quality control and the decontamination of polluted waters and soils"), the first author was able to
spend the whole November 2017 in India, having participated in a collaborative study entitled 'Decontamination of
SHOS Raša coal and soil polluted by Raša coal using bacterial biomass: a case study of coal and soil from the Labin city
area (North Adriatic, Croatia)', and discussed with colleagues (BHU, Dptm. of Geology, Varanasi, Uttar Pradesh)
further steps towards a joint environmental scientific work on a Croatian locality polluted with SHOS Raša coal.
Author(s) contribution
Gordana Medunić initialised an idea on the topic of the paper, and together with Ankica Rađenović summarised
papers on Croatian and world research. Deepti Mondol and Sadhana Nazir compiled papers on Indian research. The
all authors equally participated in typing and editing the manuscript.